Assessment of Bacterial Pathogens in Young Children with Acute Otitis Media: A Prospective Cohort Study in Western Pennsylvania, 2019-2023

BACKGROUND: Since the introduction of pediatric pneumococcal conjugate vaccines (PCV) were introduced in the US in 2000, acute respiratory illnesses, including acute otitis media (AOM) due to Streptococcus pneumoniae (Spn) have declined. Pathogens associated with AOM have changed over time. METHODS: Children aged 6 through 35 months diagnosed with either AOM (Cohort 1- AOM with tympanocentesis & Cohort 2 - AOM without tympanocentesis) or upper respiratory infection (URI) without AOM (Cohort 3) were concurrently enrolled in Pittsburgh, PA. Nasal specimens were collected for all children. Middle ear fluid (MEF) specimens were obtained by tympanocentesis for children in Cohort 1. MEF and nasal specimens were tested for Spn, Haemophilus influenzae (Hflu), and Moraxella catarrhalis (Mcat). Serotypes (Spn) and susceptibility (Spn and Hflu) were determined. RESULTS: From October 2019 through August 2023, 451 children were enrolled (Cohort 1: n=57; Cohort 2: n=262; Cohort 3: n=132). For bacterial testing of MEF, 45/57 (79%) had a single pathogen detected. Pathogens detected, alone or in combination in the MEF were Hflu 32/57 (56%), Mcat 13/57 (23%) and Spn 12/57 (21%). Of participants with bacterial pathogens detected in the MEF, there was only modest concordance with the pathogens detected in the nose. Spn serotypes observed in MEF were 3, 11A, 15B, and 19A. Among nasal specimens from children with AOM (n=319), Spn, Hflu and Mcat were detected in 46%, 43%, and 70%, respectively. The majority (134/194; 69%) of Spn isolates from the nasal specimens were penicillin- susceptible; frequently observed serotypes were 3,15B, 15C, 23B/B1, 23A, and 35B. Almost 40% (63/162) of children colonized with Hflu had a β-lactamase producing isolate. CONCLUSION: Hflu was most frequently identified in MEF although sample size was small. In nasal specimens, antibiotic-resistant Hflu were common, while the majority of Spn were penicillin-susceptible. Continued surveillance could provide valuable data to guide vaccine development and therapeutic decision-making.